Electrical apparatus, such as motors and turbine generators, occasionally overheat due to shorts or other malfunctions. The longer the overheating continues the more damage is done to the apparatus. If the malfunction is detected immediately it may mean only a quick repair, but if the overheating continues, the entire machine may be damaged. Large rotating electrical apparatus is usually cooled with a hydrogen gas stream. The organic compounds in the apparatus are first to be affected by the overheating and may decompose to form particles which enter the gas stream. Monitors then detect particles in the gas stream and sound a warning or shut down the apparatus when too many particles are detected.
Special coatings may be applied to the apparatus which decompose and form detectable particles at lower temperatures than the usual organic compounds found in the apparatus. See U.S. Pat. Nos. 4,142,416; 4,108,001; 4,130,009; 4,102,809; 3,973,439; 4,102,193; 4,056,005; 3,973,438; 4,046,733; 4,046,512, 3,972,225; 4,056,006; 4,106,745; 3,957,014; 3,995,489; 3,797,353; 4,046,943; 3,973,438; and 3,995,417. The thermoparticulating compounds disclosed in these patents produce detectable signals at temperatures below 200.degree. C., which is about the maximum temperature tolerable in turbine generators before serious damage is done to the generator.
Until now efforts to identify compounds which thermoparticulated at temperatures below 200.degree. C. has proceeded by trial and error. At first it was thought that there might be a correlation between the thermoparticulating temperature and the melting point of the compound but after observations on over 500 organic compounds were made, it was discovered that there was no correlation between the melting point of a compound and its thermoparticulation temperature. Also, no correlation was discovered between the thermoparticulation temperature and the decomposition temperature of the organic compounds. And finally, there did not appear to be any correlation between the structure of the compounds and the thermoparticulation temperature.